In live marathon telecasts, a distance between a leading runner and a following runner is often announced. The announced distance between the leading and following runners is a rough distance obtained by visual measurement by an announcer or a reporter, or a distance calculated based on a time from a passage of the leading runner at a certain point to that of the following runner and running speeds of the respective runners. Therefore, the distance between the runners announced by the announcer or the reporter is not accurate. Moreover, viewers cannot visually understand the distance only by voices of the announcer or the reporter.
Japanese Patent Laid-Open No. 2003-329915 has disclosed an image pickup system which first allows manual focus for a first object and calculates a distance to the first object based on a focus lens position when an in-focus state for the first object is obtained, and then allows manual focus for a second object and calculates a distance to the second object based on a focus lens position when an in-focus state for the second object is obtained. Further, the image pickup system calculates a difference between the calculated distances to the first and second objects to display information on the difference in a superimposed manner on a video signal.
However, the image pickup system disclosed in Japanese Patent Laid-Open No. 2003-329915 requires manual focus for the respective first and second objects to calculate the distance thereto. In other words, the image pickup system cannot calculate the distance to the second object with maintaining the in-focus state for the first object that is a main image pickup subject.
Moreover, since the image pickup system disclosed in Japanese Patent Laid-Open No. 2003-329915 first calculates the distance to the first object, and then calculates the distance between the first and second objects after the manual focus for the second object is performed, an actual distance between the first and second objects may change before the distance is calculated. In other words, even if the actual distance between the first and second objects changes every second in a marathon race or the like, the image pickup system cannot reflect the change quickly to calculate the distance between the first and second objects.